Medical device for use in bodily lumens, for example an atrium

ABSTRACT

A device positionable in a cavity of a bodily organ (e.g., a heart) may discriminate between fluid (e.g., blood) and non-fluid tissue (e.g., wall of heart) to provide information or a mapping indicative of a position and/or orientation of the device in the cavity. Discrimination may be based on flow, or some other characteristic, for example electrical permittivity or force. The device may selectively ablate portions of the non-fluid tissue based on the information or mapping. The device may detect characteristics (e.g., electrical potentials) indicative of whether ablation was successful. The device may include a plurality of transducers, intravascularly guided in an unexpanded configuration and positioned proximate the non-fluid tissue in an expanded configuration. Expansion mechanism may include helical member(s) or inflatable member(s).

BACKGROUND Field

This disclosure is generally related to percutaneous cardiac surgery,and more particularly to percutaneously deployed medical devicessuitable for determining locations of cardiac features and/or ablatingregions of cardiac tissue.

Description of the Related Art

Cardiac surgery was initially undertaken only by performing asternotomy, a type of incision in the center of the chest, thatseparates the sternum (chestbone) to allow access to the heart. In theprevious several decades, more and more cardiac operations are performedusing percutaneous techniques, that is medical procedures where accessto inner organs or other tissue is gained via a catheter.

Percutaneous surgeries benefit patients by reducing surgery risk,complications and recovery time. However, the use of percutaneoustechnologies also raises some particular challenges. Medical devicesused in percutaneous surgery need to be deployed via narrow tubes calledcatheter sheaths, which significantly increase the complexity of thedevice structure. As well, doctors do not have direct visual contactwith the medical tools used once they are placed within the body, andpositioning the tools correctly and operating the tools successfully canoften be very challenging.

One example of where percutaneous medical techniques are starting to beused is in the treatment of a heart disorder called atrial fibrillation.Atrial fibrillation is a disorder in which spurious electrical signalscause an irregular heart beat. Atrial fibrillation has been treatedsuccessfully in open heart methods using a technique know as the “Mazeprocedure”. During this procedure, doctors create lesions in a specificpattern in the left and right atriums that eliminate the spuriouselectrical signals. Such lesions were originally created usingincisions, but are now typically created by ablating the tissue with RFenergy. The procedure is performed with a high success rate under directvision, but is relatively complex to perform percutaneously because ofthe difficulty in creating the lesions in the correct spots. Substantialproblems, potentially leading to severe adverse results, may occur ifthe lesions are placed incorrectly.

Key factors which are needed to dramatically improve the percutaneoustreatment of atrial fibrillation are enhanced methods for deployment,positioning, and operation of the treatment device. It is particularlyimportant to know the position of the elements which will be creatingthe lesions relative to cardiac features such as the pulmonary veins andmitral valve.

Several methods have been previously developed for positioningpercutaneously deployed medical devices with the heart. However, thereare significant challenges associated with each of these methods. Onemethod is to map the inside of the atrium by sensing electrical activityon the atrium wall. Devices that use such a method require intimateelectrical contact with the atrium wall which is not always possiblebecause of scar tissue and deposits. Also, such devices fail toaccurately map the edges of the openings where the veins enter theatrium, which is important for correct placement of the ablationpattern. Other methods, such as using an array of ultrasonictransducers, are not practical as devices that make use of such methodswill not fit through a catheter of a reasonable size (6-8 mm diameter).Yet another method for positioning the treatment device is to make useof an external system for providing navigation, such as a magneticpositioning system. These systems are very expensive and have difficultydelivering the resolution and accuracy needed for correct placement ofablation.

Atrial fibrillation is but one example of a cardiac surgery thatrequires improved navigation and deployment for percutaneous treatment.There are many others that require similar improvement, such as mitralvalve repair.

Thus, there is a need for methods and apparatus that improve navigationand percutaneous deployment of medical devices, as well as determinationof the relative position of cardiac features such as pulmonary veins andthe mitral valve with respect to a medical device. There is a furtherneed for methods and apparatus that allow the formation of lesions in aspecified position relative to cardiac features such as pulmonary veinsand the mitral valve.

BRIEF SUMMARY OF THE INVENTION

The present design of a medical device with enhanced capabilities fordeployment, positioning and ablating within the heart employs a methodfor distinguishing tissue from blood and may be used to deliver superiorpositional information of the device relative to ports in the atrium,such as the pulmonary veins and mitral valve. The device may employmethods such as blood flow detection, impedance change detection ordeflection force detection to discriminate between blood and tissue. Thedevice may also improve ablation positioning and performance by usingthe same elements for discriminating between blood and tissue as areused for ablation. Other advantages will become apparent from theteaching herein to those of skill in the art.

At least one embodiment may be summarized as a method of operating amedical system including sensing at least one characteristic by each ofa number of transducer elements carried by a device located in at leasta portion of a bodily organ, the at least one characteristic indicativeof at least one of a presence of a fluid (e.g., blood) and a presence ofnon-fluid tissue (e.g., wall of heart); computationally discriminatingbetween the fluid and the non-fluid tissue based at least in part on theat least one characteristic sensed by at least some of the transducerelements; and providing information indicative of at least a position ofthe device in the bodily organ based on the computational discriminationbetween the fluid and the non-fluid tissue.

The method may further include ablating a portion of the non-fluidtissue in a bodily organ, for example the heart. The method may furtherinclude sensing an electrical potential of the non-blood tissue in theheart at least once after the ablating; and producing an indicationbased on the sensed electrical potential of the non-blood tissueindicative of whether the ablating was successful. Sensing at least onecharacteristic by each of a number of transducer elements may includesensing a permittivity of the fluid or the non-fluid tissue at each of aplurality of frequencies. Sensing at least one characteristic by each ofa number of transducer elements may include sensing a force exerted onthe sensor by the fluid or non-fluid tissue. Providing informationindicative of at least a position of the device in the bodily organbased on the computational discrimination between the fluid and thenon-fluid tissue may include providing information indicative of athree-dimensional pose of the device with respect to at least theportion of a heart. The method may further include intravascularlyguiding the device to a desired position while at least a portion of thedevice is in an unexpanded configuration; selectively moving at leastthe portion of the device into an expanded configuration to position thetransducer elements at least proximate the non-fluid tissue; selectivelymoving at least the portion of the device into the unexpandedconfiguration; and intravascularly retrieving the device from thedesired position while at least a portion of the device is in theunexpanded configuration.

At least one embodiment may be summarized as a medical system includinga device positionable in at least a portion of a bodily organ (e.g., aheart), the device including a plurality of transducer elements, atleast some of the transducer elements responsive to at least onecharacteristic indicative of a presence of either a fluid (e.g., blood)or non-fluid tissue (e.g., wall of heart) a computing system having atleast one processor and at least one memory that stores instructions,the computing system configured to computationally discriminate betweenthe fluid and the non-fluid tissue based at least in part on the atleast one characteristic sensed by at least some of the transducerelements; and at least one transducer configured to provide informationindicative of at least a position of the device in the bodily organbased on the computational discrimination between the fluid and thenon-fluid tissue.

The system may further include an ablation source, wherein at least someof the transducer elements may be coupled to an ablation source andselectively operable to ablate a portion of the non-fluid tissue in theheart. At least some of the transducer elements that are responsive toat least one characteristic indicative of a presence of either the fluidor the non-fluid tissue in the bodily organ may also be responsive toelectrical potential of the non-fluid tissue. At least some of thetransducer elements may be responsive to electrical potentials of thenon-fluid tissue, and the computing system may be further configured toproduce an indication indicative of whether the ablation was successfulbased on at least one sensed electrical potential of the non-fluidtissue. At least a portion of the device may be selectively moveablebetween an unexpanded configuration and an expanded configuration, thedevice sized to be delivered intravascularly when at least the portionof the device is in the unexpanded configuration, and the transducerelements positioned sufficient proximate the non-fluid tissue to sensethe at least one characteristic in the expanded configuration. Thesystem may further include a catheter having a proximal end and a distalend opposed to the proximal end, the device coupled to the catheter atthe distal end thereof; at least one communications path communicativelycoupling the transducer elements and the computing system, thecommunications path including a multiplexer and a demultiplexer, themultiplexer on a computing system side of the communications path andthe demultiplexer on a device side of the communications path.

At least one embodiment may be summarized as a method of operating adevice in at least a portion of a heart, including sensing at least onecharacteristic by each of a number of transducer elements carried by thedevice located in at least the portion of the heart, the at least onecharacteristic indicative of at least one of a presence of blood and apresence of non-blood tissue; computationally discriminating between theblood and the non-blood tissue based at least in part on the at leastone characteristic sensed by at least some of the transducer elements;providing information indicative of a position of the device in theheart based on the discrimination between the blood and the non-bloodtissue; sensing an electrical potential of the non-blood tissue in theheart; and providing an indication based on the sensed electricalpotential of the non-blood tissue.

The method may further include ablating a portion of the tissue in theheart, wherein sensing an electrical potential of the non-blood tissuein the heart may occur at least once after the ablating. The method mayfurther include evaluating the sensed electrical potential of thenon-blood tissue in the heart to determine whether the ablating wassuccessful.

At least one embodiment may be summarized as a medical system includinga device positionable in at least a portion of a heart, the deviceincluding a plurality of transducer elements at least some of thetransducer elements responsive to at least one characteristic indicativeof at least one of a presence of blood and a presence of non-bloodtissue and at least some of the transducer elements responsive to anelectrical potential of the non-blood tissue in the heart; a computingsystem having at least one processor and at least one memory that storesinstructions, the computing system configured to computationallydiscriminate between the blood and the non-blood tissue based at leastin part on the at least one characteristic sensed by at least some ofthe transducer elements; and at least one transducer configured toprovide information indicative of a position of the device in the heartbased on the computational discrimination between the blood and thenon-blood tissue and provide an indication based on the sensedelectrical potential of the non-blood tissue.

The system may further include an ablation source, wherein at least someof the transducer elements may be coupled to an ablation source andselectively operable to ablate a portion of the non-blood tissue in theheart. The system may further include a switch operable to selectivelycouple the transducer elements between an ablation mode and a sensemode, where the transducer elements may ablate the non-blood tissue inthe ablation mode and may sense the at least one characteristic in thesense mode. At least some of the transducer elements that are responsiveto at least one characteristic indicative of a presence of either bloodor non-blood tissue may also be responsive to electrical potential ofthe non-blood tissue. At least a portion of the device may beselectively moveable between an unexpanded configuration and an expandedconfiguration, the device sized to be delivered intravascularly when atleast the portion of the device is in the unexpanded configuration, andthe device sized to position the transducer elements sufficientlyproximate the non-blood tissue to sense the at least one characteristicin the expanded configuration. The transducer elements may include atleast one of a conductive trace on a flexible electrically insulativesubstrate, a conductive wire, a conductive tube, a carbon fiber materialand a polymeric piezoelectric material. The device may include a numberof flexible electrically insulative substrates that deform between anunexpanded configuration and an expanded configuration.

At least one embodiment may be summarized as a device to be insertedintravascularly, including a shaft moveable with respect to a cathetermember; at least a first helical member configured to move between aradially unexpanded configuration and a radially expanded configurationin response to the movement of the shaft with respect to the catheter,the device sized to be delivered intravascularly when at least the firsthelical member is in the unexpanded configuration; and a plurality oftransducer elements that move in response to the movement of the firsthelical member between the radially unexpanded configuration and theradially expanded configuration, at least some of the transducerelements responsive to a characteristic of at least one of a fluid and anon-fluid tissue.

The device may further include at least a second helical memberconfigured to move between a radially unexpanded configuration and aradially expanded configuration in response to the movement of the shaftwith respect to the catheter. The first helical member may carry some ofthe transducer elements and the second helical member may carry some ofthe transducer elements. The first helical member may be disposedradially spaced about the shaft. The first helical member may be woundin one of a clockwise or a counterclockwise orientation with respect tothe shaft and the second helical member may be wound in the other of theclockwise or the counterclockwise orientation with respect to the shaft.The device may further include a number of elongated ribs physicallycoupled between a proximate and a distal end of the first helicalmember. The elongated ribs may each form a respective flexibleelectrically insulative substrate and at least some of the transducerelements may comprise respective electrically conductive traces carriedby the flexible electrically insulative substrate. The shaft may beaxially moveable with respect to the catheter member between an extendedposition and a withdrawn position, a distal end of the shaft spacedrelatively closer to an end of the catheter member in the withdrawnposition than in the extended position, where the first helical memberis in the unexpanded configuration when the shaft is in the extendedposition and is in the expanded configuration when the shaft is in thewithdrawn position. The shaft may be rotatably moveable with respect tothe catheter member between an extended position and a withdrawnposition, a distal end of the shaft spaced relatively closer to an endof the catheter member in the withdrawn position than in the extendedposition, where the first helical member is in the unexpandedconfiguration when the shaft is in the extended position and is in theexpanded configuration when the shaft is in the withdrawn position. Theshaft may extend at least partially through a lumen of the cathetermember to allow manipulation of the device from a position externallylocated from a patient. At least some of the transducer elements may beresponsive to convective cooling from a flow of blood over thetransducer elements. At least some of the transducer elements may beresponsive to a permittivity at each of a plurality of frequencies. Atleast some of the transducer elements may be responsive to a force. Atleast some of the transducer elements may comprise a polymericpiezoelectric material. At least some of the transducer elements may beresponsive to an electrical potential of a portion of the non-bloodtissue. At least some of the transducer elements may include anelectrically conductive trace carried by a flexible electricallyinsulative substrate. The first helical member may form a flexibleelectrically insulative substrate and at least some of the transducerelements may comprise respective electrically conductive traces carriedby the flexible electrically insulative substrate. At least some of thetransducer elements may include an electrically conductive wire. Atleast some of the transducer elements may include an electricallyconductive tube. At least some of the transducer elements may include anelectrically conductive carbon fiber.

At least one embodiment may be summarized as a method of operating adevice including at least a first helical member and a plurality oftransducer elements that are responsive to at least one characteristicof non-blood tissue, comprising: guiding a device in an unexpandedconfiguration intravascularly to a desired position; and expanding atleast the first helical member of the device into an expandedconfiguration such that the plurality of transducer elements arepositioned to sense the at least one characteristic over a substantialportion of the non-blood tissue.

The expanding at least the first helical member may include axiallymoving a shaft that extends at least partially through a lumen of acatheter member in a first direction. The expanding at least firsthelical member may include rotatably moving a shaft that extends atleast partially through a lumen of a catheter member in a firstdirection. The method may further include retracting at least the firsthelical member into the unexpanded configuration; and intravascularlyguiding the device in the unexpanded configuration to remove the device.The retracting at least the first helical member into the unexpandedconfiguration may include at least one of axially or radially moving theshaft that extends at least partially through the lumen of the cathetermember in an opposite direction than moved when expanded.

At least one embodiment may be summarized as a medical device, includingat least a first inflatable member having at least one chamber and atleast one port that provides fluid communication with the chamber, thefirst inflatable member configured to move between an unexpandedconfiguration and an expanded configuration in response to a change of apressure in the chamber, the device sized to be deliveredintravascularly when at least the first inflatable member is in theunexpanded configuration; a plurality of transducer elements that movein response to the movement of the first inflatable member between theradially unexpanded configuration and the radially expandedconfiguration, at least some of the transducer elements responsive to acharacteristic of at least one of a fluid and a non-fluid tissue.

The first inflatable member may have at least one passage that providesfluid communication across the first inflatable member. The at least onepassage may provide fluid communication between an upstream position anda downstream position with respect to a position of the inflatablemember when positioned in a cardiovascular structure. The at least onepassage may be formed by a reinforced portion of the first inflatablemember. The reinforced portion of the first inflatable member mayinclude at least a rib, an elastic member, and a thickened portion of awall that forms the passage. The port may be coupled to a lumen of acatheter member to allow fluid communication with the chamber from afluid reservoir that is externally located with respect to a patient. Atleast some of the transducer elements may be responsive to convectivecooling from a flow of blood over the transducer elements. At least someof the transducer elements may be responsive to a permittivity at eachof a plurality of frequencies. At least some of the transducer elementsmay be responsive to a force. At least some of the transducer elementsmay comprise a polymeric piezoelectric material. At least some of thetransducer elements may be responsive to an electrical potential of aportion of the non-blood tissue. At least some of the transducerelements may include an electrically conductive trace carried by aflexible electrically insulative substrate. The first helical member mayform a flexible electrically insulative substrate and at least some ofthe transducer elements may comprise respective electrically conductivetraces carried by the flexible electrically insulative substrate. Atleast some of the transducer elements may include an electricallyconductive wire. At least some of the transducer elements may include anelectrically conductive tube. At least some of the transducer elementsmay include an electrically conductive carbon fiber.

At least one embodiment may be summarized as a method of operating adevice including at least a first inflatable member and a plurality oftransducer elements that are responsive to at least one characteristicof non-blood tissue, comprising: guiding a device in an unexpandedconfiguration intravascularly to a desired position; and inflating atleast the first inflatable member of the device into an expandedconfiguration such that the plurality of transducer elements arepositioned to sense the at least one characteristic over a substantialportion of the non-blood tissue.

Inflating at least the first helical member may include providing afluid to a chamber of the first inflatable member through a lumen of acatheter member. The method may further include deflating at least thefirst inflatable member into the unexpanded configuration; andintravascularly guiding the device in the unexpanded configuration toremove the device. Deflating at least the first helical member into theunexpanded configuration may include removing the fluid from the chamberthrough the lumen of the catheter member.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elementsor acts. The sizes and relative positions of elements in the drawingsare not necessarily drawn to scale. For example, the shapes of variouselements and angles are not drawn to scale, and some of these elementsare arbitrarily enlarged and positioned to improve drawing legibility.Further, the particular shapes of the elements as drawn, are notintended to convey any information regarding the actual shape of theparticular elements, and have been solely selected for ease ofrecognition in the drawings.

FIG. 1 is a cutaway diagram of a heart showing a medical deviceaccording to one illustrated embodiment percutaneously placed in a leftatrium of the heart.

FIG. 2 is a schematic diagram of a treatment system according to oneillustrated embodiment, including, a control unit, a display, and amedical device having an expandable frame and a leaf shaped assembly ofelements.

FIG. 3 is a broken isometric diagram of a portion of an atrium and anumber of elements showing how the elements can sense convective coolingto locate a position of ports.

FIG. 4A is a top plan view of element construction for flow sensing.

FIG. 4B is a top plan view according to yet another illustratedembodiment

FIG. 4C is a top plan view according to yet another illustratedembodiment.

FIG. 4D is a top plan view according to yet another illustratedembodiment.

FIG. 4E is a top plan view according to yet another illustratedembodiment.

FIG. 4F is a top plan view according to yet another illustratedembodiment.

FIG. 4G is a top plan view according to yet another illustratedembodiment.

FIG. 4H is a top plan view according to yet another illustratedembodiment.

FIG. 5 is a diagram showing how common leads can be shared by elementsused for flow sensing.

FIG. 6A is a schematic diagram showing an example of techniques used toimprove precision in measuring voltage drops across elements.

FIG. 6B is a schematic diagram showing an example of techniques used toimprove precision in measuring voltage drops across elements.

FIG. 6C is a schematic diagram showing an example of techniques used toimprove precision in measuring voltage drops across elements.

FIG. 7 is a circuit diagram of an example of a system used for flowsensing, port location, and tissue ablation.

FIG. 8 is a circuit diagram of a second example of a system used forflow sensing, port location, and tissue ablation.

FIG. 9 is a circuit diagram of a third example of a system used for flowsensing, port location, and tissue ablation.

FIG. 10A is a top plan view of a structure having distinct permittivitysensor elements, temperature sensor elements and ablation elements,according to one illustrated embodiment.

FIG. 10B is a top plan view of a structure having integratedpermittivity sensor and ablation elements, according to one illustratedembodiment.

FIG. 10C is a top plan view of a structure having integratedpermittivity sensor and ablation elements, according to anotherillustrated embodiment.

FIG. 10D is a top plan view of a structure having integratedpermittivity and temperature sensor and ablation elements, according toone illustrated embodiment.

FIG. 11 is a circuit diagram of an example of a system used forpermittivity sensing, port location, and tissue ablation.

FIG. 12A is a top plan view of a structure having distinct force sensorelements, temperature sensor elements and ablation elements, accordingto one illustrated embodiment.

FIG. 12B is top plan view of a structure having force sensor elementsthat are distinct from integrated temperature sensor and ablationelements, according to one illustrated embodiment.

FIG. 12C is a top plan view of a leaf shaped structure having forcesensor elements that are distinct from integrated temperature sensor andablation elements, according to one illustrated embodiment.

FIG. 13 is a circuit diagram of an example of a system used for forcesensing, port location, and tissue ablation.

FIG. 14A is an example of a frame using multiple helix shaped members.

FIG. 14B is an example of a frame using multiple helix shaped members.

FIG. 15A is an example of a frame using a single helix shaped member andmultiple ribs.

FIG. 15B is an example of a frame using a single helix shaped member andmultiple ribs

FIG. 15C is an example of a frame using a single helix shaped member andmultiple ribs.

FIG. 16A is an example of an inflatable frame with ports for blood flow.

FIG. 16B is an example of an inflatable frame with ports for blood flow.

FIG. 17A is a top plan view of a joint assembly structure, according toone illustrated embodiment.

FIG. 17B is a top plan view of a joint assembly structure, according toanother illustrated embodiment.

FIG. 17C is a top plan view of a joint assembly structure, according toanother illustrated embodiment.

FIG. 17D is a top plan view of a joint assembly structure, according toanother illustrated embodiment.

FIG. 17E is a top plan view of a joint assembly structure, according toanother illustrated embodiment.

FIG. 18A is a top plan view of a joint assembly structure, according toanother illustrated embodiment.

FIG. 18B is a top plan view of a joint assembly structure, according toanother illustrated embodiment.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various embodiments of theinvention. However, one skilled in the art will understand that theinvention may be practiced without these details. In other instances,well-known structures associated with RF ablation and electroniccontrols such as multiplexers have not been shown or described in detailto avoid unnecessarily obscuring descriptions of the embodiments of theinvention.

Unless the context requires otherwise, throughout the specification andclaims which follow, the word “comprise” and variations thereof, suchas, “comprises” and “comprising” are to be construed in an open,inclusive sense, that is as “including, but not limited to.”

The word “ablation” should be understood to mean any disruption tocertain properties of the tissue. Most commonly the disruption is to theelectrical conductivity and is achieved by heating, which could beeither resistive or by use of Radio Frequencies (RF). Other properties,such as mechanical, and other means of disruption, such as optical, areincluded when the term “ablation” is used.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the present invention. Thus, the appearances of thephrases “in one embodiment” or “in an embodiment” in various placesthroughout this specification are not necessarily all referring to thesame embodiment. Furthermore, the particular features, structures, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contentclearly dictates otherwise. It should also be noted that the term “or”is generally employed in its sense including “and/or” unless the contentclearly dictates otherwise.

The headings provided herein are for convenience only and do notinterpret the scope or meaning of the claimed invention.

Overview of Device and Mapping Methods

Various embodiments of percutaneously or intravascularly deployedmedical devices are described herein. The medical devices are capable ofexpanding into a cavity within a body and sensing characteristics (e.g.,convective cooling, permittivity, force) that distinguish between bloodand non-blood tissue. Such sensed characteristic allow a medical systemto map the cavity, for example using positions of openings or ports intoand out of the cavity to determine a position and/or orientation (i.e.,pose) of the medical device in the cavity. The medical devices may alsobe capable of ablating tissue in a desired pattern within the cavity.The medical devices may further be capable of sensing characteristics(e.g., electrical activity), indicative of whether ablation has beensuccessful.

An example of the mapping performed by the medical treatment deviceswould be to locate the position of the four openings leading to thepulmonary veins as well as the mitral valve on the interior surface ofthe left atrium. The mapping is based on locating such openings bydifferentiating between blood and non-blood tissue. There are many waysto differentiate non-blood tissue from a liquid such as blood or todifferentiate non-blood tissue from an opening in case a liquid is notpresent. By the way of example, three approaches will be detailed in thedisclosure:

1. One approach to determining the locations is to use the convectivecooling of heated transducer elements by the blood. A slightly heatedmesh of transducer elements positioned adjacent to the non-blood tissuethat forms walls of the atrium and across the openings or ports of theatrium will be cooler at the areas which are spanning the openings orports carrying blood flow.

2. Another approach to determining the locations is to make use of thediffering change in dielectric constant as a function of frequencybetween blood and non-blood tissue. A set of transducer elementspositioned around the non-blood tissue that forms the interior surfaceof the atrium and across the openings or ports of the atrium monitor theratio of the dielectric constant from 1 KHz to 100 KHz. Such can be usedto determine which of those transducer elements are not proximate tonon-blood tissue, which is indicative of the locations of openings orports.

3. Yet another approach to determining the locations is to sense aposition of the non-blood tissue that forms the atrium walls usingtransducer elements that sense force (i.e., force sensors). A set offorce detection transducer elements positioned around the non-bloodtissue that forms the interior surface of the atrium and across theopenings or ports of the atrium can be used to determine which of thetransducer elements are not in contact with the non-blood tissue, whichis indicative of the locations of openings or ports.

FIG. 1 shows a medical device 100 useful in diagnosing and/or treating abodily organ, for example a heart 102, according to one illustratedembodiment.

The medical device 100 may be percutaneously and/or intravascularlyinserted into a portion of the heart 102, for example in a left atrium104 of the heart 102. In this example, the medical device is deliveredvia a catheter 106 inserted via the superior vena cava 108 andpenetrating the transatrial septum 110 from a right atrium 112.

The catheter 106 may include one or more lumens 114. The lumen(s) 114may carry one or more communications and/or power paths, for example oneor more wires 116. The wires 116 provide connections to the medicaldevice 100 that are accessible externally from a patient in which themedical device 100 is inserted.

As discussed in more detail herein, the medical device 100 comprises aframe 118 which expands (shown in expanded configuration in FIG. 1) upondelivery to the left atrium 104 to position a plurality of transducerelements 120 (only three called out in FIG. 1) proximate the interiorsurface or non-blood tissue 122 of the left atrium 104. At least some ofthe transducer elements 120 of the medical device are used to sense aphysical characteristic of blood and/or tissue that may be used todetermine a position and/or orientation or pose of the medical device100 in the left atrium 104. For example, the transducer elements 120 maybe used to determine a location of pulmonary vein ostiums 124 and/or amitral valve 126. At least some of the transducer elements 120 of themedical device 100 may be used to selectively ablate non-blood tissue,for example portions of the interior surface 122 of the left atrium 104.For example, some of the elements may be used to ablate a pattern aroundthe openings, ports or pulmonary vein ostiums 124, for instance toreduce or eliminate the occurrence of atrial fibrillation.

FIG. 2 shows a medical device 200 according to one illustratedembodiment.

The medical device 200 takes the form of an expandable electrode grid orarray 202, including a plurality of flexible strips 204 (three calledout in FIG. 2). A plurality of transducer elements 206 (four called outin FIG. 2) form a two- or three-dimensional grid or array capable ofmapping the inside surface of a cavity or lumen without requiringmechanical scanning. An expandable frame 208 may be used to forceflexible strips 204 against the inside walls of the cavity. Theexpandable frame 208 may include one or more resilient members. Forexample, the expandable frame 208 may consist of or include a shapememory material, for instance Nitinol. Such may be useful for bothaccurate location of the parts, position and/or orientation (i.e., pose)and/or for successful ablation of a desired pattern.

The expandable frame 208, as well as flexible strips 204 can bedelivered and retrieved via a catheter member, for example a cathetersheath introducer 210, which in some embodiments may have a diameter ofabout 8 mm or smaller. Flexible strips 204 may be made of one or morethin layers of Kapton (polyimide), for instance 0.1 mm thick. Transducerelements (e.g., electrodes and/or sensors) 206 may be built on theflexible strips 204 using standard printed circuit board processes. Anoverlay of a thin electrical insulation layer (e.g., Kapton about 10-20microns thick) may be used to provide electrical insulation, except inareas needing electrical contact to blood and non-blood tissue. In someembodiments, the flexible strips 204 can form an elongated cable 216 ofcontrol leads 218, for example by stacking multiple layers, andterminating in a connector 220. The electrode grid or array 202 istypically disposable.

The medical device 200 may communicate with, receive power from and/orbe controlled by a control system 222. The control system 222 mayinclude a computing system 224 having one or more processors 226 and oneor more memories 228 that store instructions that are executable by theprocessors 226 to process information received from the medical device200 and/or to control operation of the medical device 200, for exampleactivating selected transducer elements 206 to ablate non-blood tissue.The control system 222 may include an ablation source 230. The ablationsource 230 may, for example, provide electrical power, light or lowtemperature fluid to the selected transducer elements to cause ablation.The control system 222 may also include one or more user interface orinput/output (I/O) devices, for example one or more displays 232,speakers 234, keyboards, mice, joysticks, track pads, touch screens orother transducers to transfer information to and from a user, forexample a care provider such as a medical doctor or technician. Forexample output from the mapping process may be displayed on a display232.

While the disclosed systems are described with examples of cardiacmapping, the same or similar systems may be used for mapping otherbodily organs, for example gastric mapping, bladder mapping, arterialmapping and mapping of any lumen or cavity into which the medical device204 may be introduced.

The term “transducer element” in this disclosure should be interpretedbroadly as any component capable of distinguishing between blood andtissue, sensing temperature, creating heat, ablating tissue andmeasuring electrical activity of a non-blood tissue surface, or anycombination thereof. A transducer element may be constructed fromseveral parts, which may be discrete components or may be integrallyformed.

Sensing Convective Cooling

FIG. 3 shows a portion of a medical device 300, according to oneillustrated embodiment.

The portion of the medical device 300 is particularly suitable to senseconvective cooling. The medical device 300 includes miniature transducerelements 302 a, 302 b, 302 c (collectively 302) capable of producingheat. The transducer elements 302 may, for example, be made of insulatedresistive wire, such as Nickel, or Nickel-iron composition. Theresistive wire may be mounted on an expandable frame 304. In thisembodiment, the expandable frame 304 may also be made of a material thathas high impedance. Current passed through each transducer element 302raises the temperature of the transducer element 302 by a nominalamount. A rise of 0.5-3.0 degrees Celsius above normal blood temperaturehas been found to be sufficient in most cases. The power required toraise the temperature in this particular embodiment is about 10-50 mWper transducer element 302. A central one of the transducer elements 302b, which is placed across the opening, port of ostium 306 of thepulmonary vein 308 will be cooled by blood flow more than theneighboring transducer elements 302 a, 302 c which are adjacent to theinner or interior surface or non-blood tissue 310 that forms the wall ofthe heart. Transducer elements 302 which are found to be cooler onexpandable frame 304 indicate the locations of openings or ports 306 inthe non-blood tissue 310 that forms the wall of the heart. Thisembodiment does not require intimate contact with the bodily tissue 310of the heart wall, as even a few millimetres from the openings or ports306 the cooling effect is significant compared to the cooling effect afew millimetres from the non-blood tissue 310 of the heart wall. Theback side of the transducer elements 302 may be thermally insulated forimproved performance of both sensing and ablation. Using a flat ribbonfor the expandable frame 304 may be advantageous. A cross section of aribbon expandable frame 304 may, for example have dimensions of 0.2×2 mmfor stainless steel or 0.3×2.5 mm for Nitinol. The insulation on theback side of the transducer elements 302 may take the form of a coat ofsilicone rubber.

If the transducer elements 302 are made of a material that has asignificant change in resistance with temperature, the temperature dropcan be determined from the resistance of the transducer element 302. Theresistance can be determined by measuring the voltage across thetransducer element 302 for a given current, or alternatively bymeasuring the current across the transducer element 302 for a givenvoltage, for example via a Wheatstone bridge circuit. Thus, someembodiments may take advantage of convective cooling by the flow ofblood, at least some of the transducer elements 302 functioning as a hotwire anemometer. Nickel wire is a suitable material to use, as nickel isinert, highly resistive and has a significant temperature coefficient ofresistance (about 0.6% per deg C.). Since the resistance of thetransducer elements 302 is low (typically less than 5 ohm), theelectrical noise is very low and temperature changes as low as 0.1-1 degcan be detected. There are several techniques to improve on thissensitivity. One method is to sample the voltage waveform insynchronization with the heart rate. Another is to remove the averagevoltage via AC coupling and only amplify the voltage change orderivative. Yet another method to reduce the electrical noise is to passthe signal through a digital band pass filter having a center frequencytracking the heart rate.

FIGS. 4A-4G show examples of alternative ways of constructing transducerelements. Each of the embodiments of FIGS. 4A-4F show transducerelements which have been constructed using printed circuit board (PCB)substrates. These transducer elements may be affixed to a structuresimilar to the expandable frame 208 shown in FIG. 2, which may be madefrom a material such as Nitinol. Alternatively, the PCB substrates maybe of such a thickness that the PCB substrates can form the expandableframe. The PCB substrates should be flexible enough to conform to thenon-blood tissue, but stiff enough such that the PCB substrate does notbuckle. PCB substrates may, for example, be made from Kapton®. A PCBsubstrate made of Kapton® having a thickness, for instance, ofapproximately 0.1 to 0.3 mm may be suitable. The transducer elementscould also be constructed using discrete components. FIGS. 4G-4H showembodiments that do not employ PCB substrates.

FIG. 4A shows a PCB substrate 400 a that carries a combination oftransducer elements, in particular sensor transducer elements 402 a, 402b (collectively 402, only two called out in FIG. 4A) which senseconvective cooling and ablation transducer elements 404 a, 404 b(collectively 404, only two called out in FIG. 4A) which are operable toablate non-blood tissue. Leads, collectively 406, extend to respectiveones of the transducer elements 402, 404. The leads 406 may be coupledto a control system (e.g., control system 222 of FIG. 2), which mayprovide communications, power and/or control with the transducerelements 402, 404.

FIG. 4B shows a PCB substrate 400 b that carries a number of combinedsensor and ablation transducer elements 408 a, 408 b (collectively 408,only two called out in FIG. 4B) that both sense flow and ablatenon-blood tissue. Such a feature may be a significant advantage since amedical device with combined sensor and ablation transducer elements 408can measure flow at the exact spot that ablation will occur, whilerequiring fewer parts, thus improving precision and reducing size. Inthis embodiment, each combined sensor and ablation transducer element408 has respective leads, collectively 410, coupled to a control system(e.g., control system 222 of FIG. 2).

A combined sensor and ablation transducer element 408 that can be usedfor both sensing flow and ablating can be made using standard PCBconstruction processes. For example, a 2-4 mil copper trace on a Kapton®substrate can be used. Copper changes resistance sufficiently withtemperature to be used to determine blood flow in the manner discussedabove. Copper can also be used as an ablation element by applyingsufficient current through the copper to cause the combined sensor andablation transducer element 408 to heat resistively, for example to atemperature above 60° C. Power in the range of approximately 130-250 mWdelivered to a copper pattern that has external dimensions of 3 mm×10 mmand is thermally insulated on the side away from the non-blood tissuemay be sufficient to transmurally ablate a 3 mm deep section of thenon-blood tissue that forms the atrium wall. In this approach, thenon-blood tissue is heated by conduction from the copper combined sensorand ablation transducer element 408. When heating the non-blood tissueby conduction, the combined sensor and ablation transducer element 408may be electrically insulated from the non-blood tissue.

Alternatively, the combined sensor and ablation transducer element 408can also be used to ablate non-blood tissue by using the combined sensorand ablation transducer element 408 as an electrode for delivering RFenergy to the non-blood tissue. In this scenario, electrical current istransferred directly to the non-blood tissue and the non-blood tissue isresistively heated by the current flow. When delivering RF energy, apreferred method may be to have low electrical impedance between thecombined sensor and ablation transducer element 408 and the non-bloodtissue. Delivering RF energy is also possible if the combined sensor andablation transducer element 408 is capacitively coupled to the non-bloodtissue, so long as the impedance at the frequency of RF energy beingused is sufficiently low—typically under a few kilo ohms or less for acombined sensor and ablation transducer element of the size mentionedabove. Note that in the case where the combined sensor and ablationtransducer element 408 has a low electrical impedance connection to thenon-blood tissue for low frequencies, it is also possible to use thecombined sensor and ablation transducer element 408 to sense anelectrical potential in the non-blood tissue that forms the heart wall,for example to generate an electro-cardiogram. Thus it is possible forthe same combined sensor and ablation transducer element 408 to senseflow, sense electrical potential of the non-blood tissue that forms theheart wall, and ablate non-blood tissue.

FIG. 4C shows a PCB substrate 400 c that carries a number of combinedflow sensor, ablation and temperature transducer elements 412 a, 412 b(collectively 412, only two called out in FIG. 4C) that can be used tosense flow, ablate non-blood tissue and sense or monitor temperature,for example for ablation control. A single control lead, collectively414, is required per combined flow sensor, ablation and temperaturetransducer element 412, plus a common return lead 416 to the multiplecombined flow sensor, ablation and temperature transducer elements 412.The combined flow sensor, ablation and temperature transducer element412 can take the form of a low resistance resistor, for example aresistor formed by a 30-100 micron wide trace of 10-30 micron copperfoil. Such a resistor has a typical resistance of 2-20 ohms and can beused as a combined flow sensor, ablation and temperature transducerelement 412 to sense flow, perform ablation and sense temperature. Whenused as a temperature sensor, the resistance changes about 1% for a 2degree C. temperature change.

FIG. 4D shows a PCB substrate 400 d that carries a number of adjacenttransducer elements 420 a, 420 b (collectively 420, only two called outin FIG. 4D). The transducer elements 420 share common control leads 422.This feature is an advantage as it dramatically reduces the number ofleads 422 needed to return to the control system (e.g., control system222 of FIG. 2).

FIG. 5 shows an expanded example of a portion of the embodiment of FIG.4D positioned proximate non-blood tissue 500. To determine flow bymeasuring the resistance of transducer element 420 b, the voltage at alead 422 a and lead 422 b should be made equal and the voltage at a lead422 c and lead 422 d should be made equal, but to a different voltagethan that of lead 422 a and lead 422 b. In this condition, negligiblecurrent will flow through transducer element 420 a and transducerelement 420 c. Therefore, the current flowing through lead 422 b andlead 422 c is the same as the current flowing through the transducerelement 420 b, and the resistance of the transducer element 420 b can becalculated in a straightforward manner using the equation V=I/R.

To cause the transducer element 420 b to heat to a temperaturesufficient to cause ablation, while not causing ablation at transducerelement 420 a and transducer element 420 c:

-   -   the voltage at lead 422 c and lead 422 d should be made equal;    -   the voltage at lead 422 b should be made higher than the voltage        at lead 422 c such that sufficient power is delivered to the        transducer element 420 b to cause the transducer element 420 b        to heat to the appropriate temperature; and    -   the voltage at lead 422 a should be set a value that is a        fraction of that at lead 422 b such that the power delivered to        the transducer element 420 a is not sufficient to cause the        temperature of the transducer element 420 a to rise enough for        tissue ablation.

For example, if the voltages at lead 422 c and lead 422 d are set to 0v, voltage at lead 422 b is set to n volts and voltage at lead 422 a isset to ⅔ n volts, the power delivered to the transducer element 420 awill be only 11% of that delivered to the transducer element 420 b. Thistechnique of having adjacent transducer elements 420 share common leads422 can, for example, be used in a elongated one-dimensional line ofconnected transducer elements 420 or may be applied to transducerelements 420 connected in two-dimensional (as illustrated in FIGS. 8,17A-17C, 18A and 18B) or three-dimensional arrays.

FIG. 4E shows a PCB substrate 400 e that carries a number of transducerelements 424 a, 424 b (collectively 424, only two called out in FIG.4E). The transducer elements 424 are coupled to leads 426, similar toleads 422 of the embodiment of FIG. 4D, and to additional leads 428,which have been added to measure the voltage at the ends of thetransducer elements 424. This feature advantageously increases theaccuracy in determining the resistance, and thus temperature, of thetransducer elements 424. The leads 426 that provide the current to thetransducer elements 424 typically have a small voltage drop across themthat can affect the accuracy of the resistance calculation of thetransducer element 424. These additional leads 428 will have a verylimited amount of current flowing through them, and thus the voltagedrop through the leads 428, even for a distance of several meters willbe negligible, and the voltage drop across the transducer elements 424can be determined accurately.

FIG. 4F shows a flexible PCB substrate 400 f that forms a leaf shapedassembly. An expandable frame (e.g., expandable frame 208 of FIG. 2) maybe covered by several of these leaf shaped assemblies, each of whichwill cover or be proximate a respective portion of the non-blood tissuethat forms the wall of the body organ when in use. Each of the leafshaped assemblies caries a plurality of transducer elements 430 a, 430 b(collectively 430, only two called out in FIG. 4F). In this example, thetransducer elements 430 are coupled together as described aboveembodiment of FIG. 4D. Leads 432 couple each transducer 430 to a controlsystem (e.g., control system 222 of FIG. 2). The leads 432 may couplepower, communications and/or control signals. The leads 432 may, forexample, provide for electrically conductive coupling, inductivecoupling, capacitive coupling, optical coupling, galvanic coupling,fluidic coupling and/or thermal coupling.

There are other approaches for creating the transducer elements that donot rely on a PCB. FIGS. 4G and 4H provide examples of some of these.

FIG. 4G shows transducer elements 440 a, 440 b (collectively 440, onlytwo called out in FIG. 4G) that are made from a bundle of carbon fibers.Leads 442 couple the transducer elements 440 to a control system.

FIG. 4H shows transducer elements 450 a, 450 b (collectively 450, onlytwo called out in FIG. 4H) that are made directly from a hollow tube ofa metal such as stainless steel or alternatively from wire. Leads 452couple the transducer elements 450 to a control system.

The structures of the embodiments of FIGS. 4G and 4H may be advantageousover other embodiments, since the structures are simple to assemble, andcan be used directly as the supporting structure itself. Leads 442, 452are connected at intervals to the carbon fibre or metal. The materialbetween the leads 442, 452 form the transducer elements 440, 450. Inorder to function properly, these transducer elements 440, 450 shouldhave the electrical properties the same as or similar to the electricalproperties indicated previously. These two embodiments provide anexample of where the same transducer element 440, 450 can sense flow,sense or measure temperature, deliver the ablation energy, and/or be anintegral component of the supporting structure.

FIGS. 4A-4H show examples of many transducer element configurations thatare possible. From the previous descriptions, it is important to notethat a single transducer element can sense blood flow in order todistinguish between blood and non-blood tissue, sense an electricalpotential of the non-blood tissue (e.g., heart wall), ablate non-bloodtissue, sense or measure temperature, and/or form an integral componentof the supporting structure, or any combination of these functions. Theablation may be performed by causing the transducer element to heat, orby delivering energy, such as RF directly to the non-blood tissue. Also,transducer elements can be constructed using individual leads, commonground lead, or shared leads. Each lead may have a separate lead thatruns in parallel to it for the purpose of accurately determining voltagepotential directly at the transducer element. As well, the examplesdiscussed methods of sensing temperature that relied on changes inresistance. However, it is certainly possible to use other temperaturesensing methods, such as thermistors or thermocouples in conjunctionwith the transducer elements that produce heat. For example, the sensingtransducer element of the embodiment of FIG. 4A could be a thermistor,thermocouple or temperature sensitive diode.

FIG. 7 shows an embodiment of an electric circuit 700 that can be usedto distinguish between blood and non-blood tissue by sensing flow ofblood.

In this example, transducer elements 702 a-702 d (collectively 702) maybe resistive elements, for example formed from copper traces on aflexible printed circuit board substrate, or resistive wires mounted ona structure. Each transducer element 702 is connected by electronictransducer selection switches 704 a-704 h (collectively 704) to a singlepair of wires 706 a, 706 b (collectively 706) that provide a path out ofthe body via a cable 708. The transducer selection switches 704 may, forexample be FET or MOSFET type transistors. The transducer selectionswitches 704 will typically need to carry significant power during theablation phase. The cable 708 may extend through a lumen of a catheteror may otherwise form part of a catheter structure.

The transducer selection switches 704 are selected by signals applied bya demultiplexer (selector) 710. The demultiplexer 710 may be controlledby a small number of wires 712 (or even a single wire if data is relayedin serial form). The wires 706, 712 extend out of the body via the cable708. The transducer selection switches 704 and the demultiplexer 710 maybe built into a catheter (e.g., catheter 106 of FIG. 1) near a distalend or point of deployment. The transducer selection switches 704 anddemultiplexer 710 may be located within or near the expandable frame(e.g., expandable frame 208 of FIG. 2) in order to minimize the numberand/or length of connecting wires extending through the catheter.

At the other or proximate end of the catheter are a mode selectionswitch 726 and multiplexer 714. The mode selection switch 726 isoperable to select between a flow sensing mode (position shown in thedrawing) and an ablation mode (second position of the mode selectionswitch 726). In flow sensing mode, a current is created by a voltagesource 716 and resistor 718 (forming an approximate current source) androuted into a transducer element 702 selected via transducer selectionswitches 704. The two transducer selection switches 704 that areconnected to a given one of the transducer elements 702 to be used tosense flow, are set to be closed and the remainder of the transducerselection switches 704 are set to be open. The voltage drop across thetransducer element 702 is measured via an Analog-to-Digital converter(ADC) 720 and fed to the control computer 722.

It may be advantageous to use alternating current or a combination ofalternating current and direct current for sensing and ablation. Forexample, direct current for ablation and alternating current forsensing. Alternating current approaches may also prevent errors fromelectrochemical potentials which could be significant if differentmetals come in touch with blood.

Determination of the location of the openings or ports into the chambermay be achieved by turning on all of transducer elements 702sequentially or in groups and determining a temperature by measuring theresistance of each transducer element 702. A map of the temperature ofthe transducer elements 702 may be formed in control computer 722 or thecontrol computer 722 may otherwise determine a position and/ororientation or pose of the device in the cavity. The transducer elements702 with lower temperatures correspond to the openings or ports leadingto the veins or valves.

When mode selection switch 726 is set to select ablation, an ablationpower source 724 is connected sequentially to the transducer elements702 that are selected by the control computer 722 by addressing themultiplexer 714, which in turn controls the transducer selectionswitches 704 via the demultiplexer 710. The ablation power source 724may be an RF generator, or it may be one of several other power sources,several of which are described below. If ablation power source 710 is anRF generator, the configuration of FIG. 7 implies unipolar RF ablation,in which current is fed into the non-blood tissue and passes to a groundconnected to the body. The current that passes through the non-bloodtissue causes the non-blood tissue to heat. However, bipolar ablationcan be used as well. Other sources of ablation can be used besides radiofrequency. Frequencies from DC to microwaves can be used, as well asdelivery of laser power via optical fibers or cryogenics via thin tubes.For laser ablation, the transducer selection switches 704 may take theform of optical switches. For cryogenic ablation, the transducerselection switches 704 take the form of suitable valves and/or actuators(e.g., solenoids). Alternatively, the bottom terminal of the lowerswitch of mode selection switch 726 may be coupled directly to ground.In this configuration, the ablation power source 724 can be configuredto supply current with frequencies from DC to microwave, which willcause the selected transducer elements 702 to heat directly and produceablation via thermal conduction.

During ablation it may be desirable to monitor the temperature of thenon-blood tissue. The ideal temperature range for the non-blood tissueduring ablation is typically 50-100° C. Since the example includestemperature monitoring as part of the blood flow sensing, the progressof ablation can be monitored by temporarily switching mode selectionswitch 726 to a temperature sensing position several times during theablation.

FIG. 8 shows another embodiment of a circuit 800 that can be used todistinguish between blood and non-blood tissue by sensing flow.

In this example, transducer elements 802 a-802 g (collectively 802, onlyseven called out in FIG. 8) may be resistive elements, for exampleformed from copper traces on a printed circuit board substrate, orresistive wires mounted on a structure. The ends of each transducerelement 802 are electrically coupled to the ends of adjacent transducerelements 802 to form a connected grid or array 804. Each node (indicatedin FIG. 8 by the markings A, B, C, D, E, F, G, H, and I) in the grid orarray is electrically coupled to a respective control wire, collectively806. The control wires 806 extend out of the human or animal body via acable 808, which may, for example extend through a lumen of a catheter.

The control wires 806 may be coupled to respective ones of transducerselection switches 810 a-810 i (collectively 810) at a proximate end ofa catheter. Each of the transducer selection switches 810 is controlledby a control system 812, which may, for example, take the form of aprogrammed general purpose computer, special purpose computer,applications specific integrated circuit (ASIC) or field programmablegate array (FPGA). The control system 812 applies signals to selectbetween an adjustable current source 814 a-814 i (collectively 814) andground 816 (only one called out in FIG. 8).

When a given transducer element 802 is to be used for blood flowsensing, the transducer selection switch 810 connected to the node A-Ion one end of the given transducer element 802 is set to select thecurrent source 814 and the transducer selection switch 810 connected tothe node on the other end of the given transducer element 802 isconfigured to select ground 816. All nodes connected by a transducerelement 802 to the node configured to select a current source 814 arealso configured to select a current source 814. All nodes connected by atransducer element 802 to the node configured to select a ground arealso configured to select ground 816. All of the connected currentsources 814 are adjusted to deliver the same small voltage at the nodesA-I they are connected to. For example, if the transducer element 802 eis to be used, then nodes B, D E, and H will be connected to currentsources 814 b, 814 d, 814 e, 814 h, and nodes A, C, F, G, and I will beconnected to ground 816. The connected current sources 814 b, 814 e, 814d, 814 h will be adjusted so that the voltage at nodes B, E, D, and Hwill be the same. The control system 812 controls the voltage at thenodes, for example by:

-   -   selecting the desired node with a multiplexer 818;    -   measuring the voltage with an analog to digital converter (ADC)        820;

and

-   -   adjusting the corresponding current source 814 to achieve the        desired voltage.

In this configuration, the current through all transducer elements 802connected to the given transducer element 802 e will be zero. Thereforeall current from the current source 814 e connected to the giventransducer element 802 e will pass through the transducer element 802 e.As both the voltage drop across and the current through the giventransducer element 802 e are known, the resistance can be determined andthe corresponding temperature can be determined. Determination of thelocation of the openings or ports into the cavity (e.g., chamber oratrium) may be achieved by turning on all or at least some of transducerelements 802 sequentially, and determining the temperature by measuringa resistance of each of the transducer elements 802. The control system812, or some other system, may produce a map of the temperature of thetransducer elements 802, where the lower temperatures correspond to theopenings or ports leading to veins or valves.

When a transducer element 802 is to be used for ablation, the transducerselection switch 810 connected to the node A-I on one end of the giventransducer element 802 is set to select the current source 814 and thetransducer selection switch 810 connected to the node A-I on the otherend of the given transducer element 802 is configured to select a groundconnection 816. All nodes A-I connected by a transducer element 802 toeither end of the given transducer element 802 to be used for ablationare configured to select a current source 814. The current source 814connected to the given transducer element 802 to be used for ablation isset to deliver sufficient power to the given transducer element 802 toraise its temperature to 50° C.-100° C., enough to cause non-bloodtissue ablation. All of the other connected current sources 814 areadjusted to deliver current so that the voltages at the node A-I theyare connected to is a percentage of the voltage at the node A-Iconnected to the given transducer element 802 being used for ablation.For example, if the transducer element 802 e is to be used for ablation,then nodes B, C, D, E, H, and I will be connected to current sources 814b, 814 c, 814 d, 814 e, 814 h, 814 i, and node A, F, and G will beconnected to ground 816. The current source 814 e connected to node Ewill be adjusted so that sufficient power is delivered to transducerelement 802 e to cause ablation. In doing so, a voltage will begenerated at the node E. The current sources 814 b, 814 d, 814 hconnected to nodes B, D, and H are set to ensure the voltage at thosenodes is, for example 66% of the voltage at node E. The current sources814 c, 814 i connected to nodes C and I are set to ensure the voltagesat those nodes is, for example 33% the voltage at node E. In doing do,the power delivered to all transducer elements 802 connected to nodes B,C, D, H, and I will be 11% of the power delivered to the giventransducer element 802 e, which is insufficient for ablation. It ispossible to use different percentages for voltage values than specifiedherein.

While FIG. 8 shows one current source for each element, it is alsopossible to create a circuit that uses multiplexing to reduce the numberof required current sources. Also, a circuit can be specified that usesvoltage sources instead of current sources.

There are several ways to improve the accuracy in sensing the voltagedrop across the transducer elements to improve accuracy of temperaturemeasurement or flow sensing. One approach to achieve improved accuracyis to use four terminal sensing.

FIG. 6A shows a circuit 600 a that implements four terminal sensing,according to one illustrated embodiment.

In FIG. 6A, a transducer element 602 a is coupled to power leads 604 a,604 b (collectively 604) to supply the current necessary to cause thetransducer element 602 a to heat sufficiently to be able to measureconvective cooling. Measurement leads 606 a, 606 b (collectively 606)are used to measure the voltage across the transducer element 602 a.Negligible current goes through measurement leads 606 a, 606 b and sothere is no voltage drop over the length of the measurement leads 606.

In some configurations, being able to minimize the effect of leadresistance when measuring voltage across the transducer elements ispossible without adding additional wires. FIG. 6B shows a circuit 600 bthat may implement such.

In temperature sensing or convective cooling sensing mode, leads 610 a,610 b (collectively 610) are used to supply and sink the currentnecessary to cause transducer elements 612 a-612 e (collectively 612) toproduce sufficient heat to be able to measure convective cooling. Leads614 a, 614 b are used to measure the voltage across transducer element612 a. Leads 614 b, 614 c are used to measure the voltage acrosstransducer element 612 b. Leads 614 c, 614 d are used to measure thevoltage across transducer element 612 c. Leads 614 d, 614 e are used tomeasure the voltage across transducer element 612 d. Leads 614 e, 614 fare used to measure the voltage across transducer element 612 e. Duringablation mode, leads 614 a, 614 b are used to supply the current tocause transducer element 612 a to ablate the non-blood tissue, leads 614b, 614 c are used to supply the current to cause the transducer element612 b to ablate, and so on.

FIG. 6C shows a circuit 600 c according to another illustratedembodiment. The circuit 600 c may minimize the effect of lead resistancewhen measuring voltage across the transducer elements without addingadditional wires.

As an example, the transducer element 622 a between nodes J and O isbeing used for temperature, flow, or convective cooling sensing. Theleads connected to nodes J and O supply the current to the transducerelement 622 a between the nodes. This causes a measurable voltage dropacross the transducer element 622 a between nodes J and O. The leadsattached to nodes B, D, E, F, I, K, N, P, S, T, U, W are used to sensevoltage at the respective nodes. The control system to which the leadsare attached is configured so that there is negligible current flowthrough these leads, and negligible voltage drop across the leads. Theleads attached to nodes A, C, G, H, L, M, Q, R, V, and X are activelydriven and drive the nodes to a particular voltage. The control systemadjusts the voltages at nodes A, C, G, H, and L so that the voltagemeasured at nodes B, D, E, F, I, and K are all measured to be equal.When this state occurs, the current between nodes E and D, E and B, Eand F is negligible and therefore, the current between nodes E and Jmust be negligible, and node E will be at the same potential as node J.The control system adjusts the voltages at nodes X, R, V, M, and Q sothat the voltage measured at nodes W, S, T, U, N, and P are all measuredto be equal. When this state occurs, the current between nodes S and T,T and W, T and U is negligible and therefore, the current between nodesT and O must be negligible, and node T will be at the same potential asnode O. The voltage drop across the element between nodes J and O istherefore equal to the difference between the voltage at node E and thevoltage at node T.

FIG. 9 shows an embodiment that reduces the number of control leads.

FIG. 9 shows a circuit 900 that includes a plurality of transducerelements 902 a-902 i (collectively 902, only nine called out in FIG. 9)which may form a one-, two-, or three-dimensional grid or array 904. Aplurality of diodes 906 a-906 i (collectively 906, only nine called outin FIG. 9) or other non-linear devices or active devices are used toreduce the number of control leads 908. The leads 908 may be externallyaccessible from an exterior of a patient, for example via a cable 910that extends through a lumen of a catheter or otherwise forms part of acatheter.

When this circuit 900 is not sensing or ablating, adjustable voltagesources 914 a-914 h (collectively 914, only eight called out in FIG. 9)are configured to reverse bias the diodes 906, so no current flows inthe circuit 900. The circuit 900 may includes a plurality of currentsensors 912 a-912 h (collectively 912), which couple signals indicativeof sensed currents to a control system 916. In this example, the reversebiasing operation is achieved by setting voltage sources 914 a-914 d topositive voltage “h” and voltage sources 914 e-914 h to ground. When atransducer element 902 is to be used for flow sensing, temperaturesensing, or ablation, the diode 906 that is in series with the giventransducer element 902 is forward biased. This is achieved by settingthe voltage source 914 that is connected to the given diode 906 to apositive voltage “g” that is greater than 0 and less than h, and settingthe voltage source 914 that is connected to the given transducer element902 to a positive voltage “f” which is greater than 0 and less than gand sufficient to forward bias the respective diode 906. For example, ifthe transducer element 902 e is to be used for sensing or ablation,adjustable voltage source 914 g should be set to g volts, adjustablevoltage source 914 b should be set to f volts, adjustable voltagesources 914 a, 914 c, 914 d should be set to h volts, and adjustablevoltage sources 914 e, 914 f, and 914 h should be set to ground where0<f<g<h. The particular values used for f, g, and h depend on suchfactors as the desired amount of heat from the transducer element 902and the resistance of the transducer element 902. Since the forwardvoltage of a silicon diode changes about 2 mV/deg C., the diodes 906 canalso be used as temperature sensors.

In some embodiments, it is beneficial to ensure the entire medicaltreatment device is electrically insulated from the body. The reasonsthat this may be desirable are to prevent electrochemical activity fromgenerating offset voltages, prevent leakage currents from affectingmeasurements and prevent gas bubble generation inside the blood stream.

Sensing Impedance Change

Measuring electrical impedance has been suggested as a way fordetermining when a catheter probe is in contact with the non-bloodtissue of the heart wall. However, distinguishing non-blood tissue fromblood using electrical impedance is problematic as the impedance isaffected by many factors such as contact pressure and contact area.Also, the transducer element (e.g., electrode) may be in contact withmany different materials, each of which has different impedance.However, using permittivity (also known as dielectric constant) measuredover a range of frequencies can be used effectively to make thedetermination between blood and non-blood tissue.

As mentioned, material such as blood, muscle tissue, fat, fibrousmaterial, and calcified tissue each has different impedance. However, inall the materials mentioned, except for blood (and other liquids such asurine) the permittivity drops with increasing frequency. For example,the conductivity of all those materials, including blood, stays nearlyconstant from DC to over 100 MHz. The permittivity of blood (and mostother liquids in the body) is about the same at 1 KHz and 100 Khz, whilein all other materials mentioned the dielectric constant drops by abouta factor of 4, and typically by at least a factor of 10 between thosetwo frequencies. Therefore, accurate discrimination between blood andnon-blood tissue can be made by monitoring the ratio of the permittivityat 1 KHz to the value at 100 KHz. Table 1 and Table 2 show the change ofConductivity and Relative Permittivity with respect to frequency.

TABLE 1 Tissue Conductivity Conductivity (S/m) log₁₀(Freq) 3 5 6 7 8Blood 0.7 0.7 0.7 1 1.49 Fat 0.025 0.025 0.03 0.04 0.06 Muscle 0.4 0.40.4 0.4 0.75 Fibrous Material 0.24 0.24 0.24 0.29 0.33 Calcium 0.08 0.080.1 0.12 0.17 Vessel Wall 0.58 0.58 0.58 0.67 0.83

TABLE 2 Tissue Relative Permittivity Relative Permittivity log₁₀(Freq) 35 6 7 8 Blood 4100 4000 2000 300 75 Fat 20000 100 50 30 12 Muscle 40000010000 8000 200 70 Fibrous Material 2000 500 50 5 3 Calcium 10500 500 25070 30 Vessel Wall 100000 5000 4000 100 30

FIGS. 10A-10D show examples of different ways that transducer elementsto sense permittivity may be constructed. FIGS. 10A-10D show examples ofvarious transducer elements which may be constructed using flexibleprinted circuit board substrates and/or materials. The resultingtransducer elements may be affixed to a structure similar to theexpandable frame 208 (FIG. 2) made from a material such as Nitinol.Alternatively, the resulting transducer elements may include PCBsubstrates of such a thickness that the PCB substrates may form theframe itself. The transducer elements could also be constructed usingdiscrete components.

FIG. 10A shows a flexible PCB substrate 1000 a that carries permittivitysensor elements 1002 (only one called out in FIG. 10A) responsive topermittivity, ablation elements 1004 (only one called out in FIG. 10A)operable to ablate, and temperature sensor elements 1006 (only onecalled out in FIG. 10A) responsive to temperature. In the illustratedembodiment, the ablation elements 1004 and temperature sensor elements1006 share some control leads 1008. Leads 1008 are coupled to a controlsystem (not illustrated in FIG. 10B). It is also possible that eachablation elements 1004 and temperature sensor elements 1006 has separatecontrol leads 1008 coupled to a control system (not illustrated in FIG.10B).

FIG. 10B shows a flexible PCB substrate 1000 b that carries combinedpermittivity sensor and ablation elements 1010 (only one called out inFIG. 10B) that both responsive to permittivity and are operable toablate tissue. The PCB substrate 1000 b also carries separatetemperature sensor elements 1012 (only one called out in FIG. 10B) thatare responsive to temperature. Leads 1114 are coupled to a controlsystem (not illustrated in FIG. 10B).

FIG. 100 shows a flexible PCB substrate 1000 c that carries combinedpermittivity and ablate elements 1016 (only one called out in FIG. 100)that both are responsive to permittivity and are operable to ablatenon-blood tissue. Each of the combined permittivity and ablate elements1016 has a respective lead, collectively 1018, extending to a controlsystem (not shown in FIG. 10C). An example of a circuit used to controland activate the combined permittivity and ablate elements 1016 is shownin FIG. 11.

FIG. 10D shows a flexible PCB substrate 1000 d that carries combinedpermittivity sensor, temperature sensor and ablation elements 1020 thatare responsive to permittivity, responsive to temperature and operableto ablate non-blood tissue. Each of the combined elements is coupled bya respective lead, collectively 1022, to a control system (notillustrated in FIG. 10D). Such an embodiment can be built using aprinted circuit board with copper traces that do not have a surfaceinsulation. The temperature sensing and ablation can be controlled aspreviously described in reference to FIG. 7. The permittivity sensingcan be controlled as will be described with reference to FIG. 11.

FIG. 11 shows a circuit 1100 that can be used to distinguish blood fromnon-blood tissue by detecting the change in permittivity, according toone illustrated embodiment.

A transducer element 1102 carried on a PCB substrate 1104 is in physicalcontact with a bodily material 1106 (non-blood tissue or blood). Thebodily material 1106 is electrically grounded to a same return path 1108as the circuit 1100. Instead of a return path, a ground electrodeadjacent to the transducer element (e.g., electrode) 1102 can be used.An alternate embodiment may be to use a balanced pair of electrodes withequal but opposite phase signals relative to ground. Such aconfiguration increases immunity to electrical noise. When frequency F₁or F₂ is fed to transducer element 1102 from oscillators 1110 a, 1110 bvia a resistor 1112 the phase shift of the signal caused by thedielectric constant of the bodily material 1106 can be measured by aphase meter. The permittivity is the tangent of the phase shift. Forbetter noise immunity both the in-phase component and the out-of-phase,or quadrature, are measured (outputs 1114 a, 1114 b) then divided todetermine the phase shift. The in-phase and out-of phase components aremeasured by multiplying the voltage signal on transducer element 1102with the driving signal and with the driving signal phase shifted by 90degrees using phase shifter 1116 and multipliers 1118. A selector 1119may be used to selectively switch between coupling the frequencies F₁,F₂, or no frequency.

A pair of analog-to-digital converters (ADC) 1120 are used to digitizethe results, after low pass filtering by capacitor 1122. If desired, thecomplete operation can be performed digitally by digitizing the signalfrom the transducer element 1102, since the highest frequency isrelatively low. A separate circuit can be used for each transducerelement 1102 or a selector 1124 (also known as multiplexer or analogswitch) can connect the same circuit to multiple transducer elements1102 in rapid succession. The time needed for an accurate measurement istypically several milliseconds; therefore even a large grid or array oftransducer elements 1102 can be mapped quickly. A same lead 1126 canalso be used to feed current for RF ablation using ablation energysource 1128 and a switch 1130. Alternatively a different power source,such as a DC current source, could be connected and provide a voltageand current for directly causing the transducer element 1102 to producea sufficient amount of heat to cause ablation.

Sensing Force

Another method of distinguishing between non-blood tissue and blood isto measure a force being exerted inwardly on one or more transducerelements mounted or otherwise carried by an expandable frame (e.g.,expandable frame 208 of FIG. 2). As an example of this approach, thetransducer elements may take the form of an array of force sensors, forexample force sensing pads. A polymeric piezoelectric material, such asPVDF, may be used as a force sensing element and two or more forcesensing elements may be combined to form a force sensing grid. Suchforce sensing elements are already commercially available, such as Ktechpart number MP-25-04-PL (from www.ktech.com). These PVDF based forcesensing pads are very thin, flexible, have high output and are easy tointegrate into a flexible printed circuit board. Liquids, such as blood,create very little resistive force when the expandable frame forces theforce sensor transducer elements outward to the non-blood tissue thatforms the interior surface of the cavity being mapped. The force sensortransducer elements located proximate to the openings or ports will besubject to less force than those proximate to the non-blood tissue. Thediffering force distribution across the force sensor transducer elementsenables the location of the openings or ports to be determined.

FIGS. 12A-12C show examples of different ways the force sensortransducer elements may be constructed using flexible printed circuitboard substrates. Force sensor transducer elements may be affixed to astructure similar to previously described expandable frames (e.g.,expandable frame 208 of FIG. 1) made from a material such as Nitinol.Alternatively, the PCB substrate may be of such a thickness that the PCBsubstrate can be the frame itself. The transducer elements could also beconstructed using discrete components.

FIG. 12A shows a flexible printed circuit board substrate 1200 a thatcarries separate force sensor transducer elements 1202 (only one calledout in FIG. 12A) responsive to force, temperature sensor transducerelements 1204 (only one called out in FIG. 12A) responsive totemperature, and ablation transducer elements 1206 (only one called outin FIG. 12A) operable to ablate non-blood tissue. The various transducerelements 1202, 1204, 1206 share a common ground 1208. The ablation andtemperature sensor transducer elements 1206, 1204, respectively, share acommon control lead 1210. Control leads 1210 are coupled to a controlsystem (not shown in FIG. 12A). The preferred force sensor transducerelement 1202 is a polymeric piezoelectric material. An example of acircuit that can be used to control and monitor such force sensortransducer elements 1202 is shown in FIG. 13.

FIG. 12B shows a flexible printed circuit board substrate 1200 b thatcarries separate force sensor transducer elements 1222 (only one calledout in FIG. 12B) responsive to force and elements with a combinedtemperature sensor and ablation transducer elements 1224 (only onecalled out in FIG. 12B). Each of the transducer elements 1222, 1224 hasrespective leads, collectively 1226, coupled to a control system (notshown in FIG. 12B). The combined temperature sensor and ablationtransducer elements 1224 can be controlled in the same way as describedfor the embodiment of FIG. 7. The force sensor transducer element 1222can be controlled and monitored as described herein with reference toFIG. 13.

FIG. 12C shows a flexible printed circuit board substrate 1200 c thatcarries force sensor transducer elements 1232 (only one called out inFIG. 12C) responsive to force, and combined or integrated temperaturesensor and ablation transducer elements 1234 (only one called out inFIG. 12C) responsive to temperature and operable to ablate non-bloodtissue. The combined temperature sensor and ablation transducer elements1234 are distinct from the force sensor transducer elements 1232. Eachof the various types of transducer elements 1232, 1234 has respectiveleads, collectively 1236, coupled to a control system (not shown in FIG.12C) possibly via a multiplexer (not shown in FIG. 12C). The combinedtemperature sensor and ablation transducer elements may be controlled inthe same way as previously discussed with reference to FIG. 7.

FIG. 13 shows an embodiment of a circuit 1300 used to sense the forcesthe force sensor transducer elements (e.g., FIGS. 12A-12C) sense,according to one illustrated embodiment.

A force is exerted on a force sensor transducer element 1302 carried bya flexible PCB substrate 1304, by a bodily material 1306, for exampleblood or non-blood tissue.

A charge amplifier 1308 converts an output of the force sensortransducer element 1302 to a voltage which is digitized by ananalog-to-digital (ADC) converter 1310. This voltage is proportional tothe force exerted on the force sensor transducer element 1302 by thebodily material 1306, and the output may be indicative of a pressure. Anablation transducer element (e.g., electrode) can be used fortemperature monitoring, as explained earlier, or a separate temperaturesensor 1312 can be used. A capacitor 1314 can be used to isolate the RFfrom the DC current used for temperature sensing. Temperature sensingmay be used by a temperature controller 1316 to control an ablationpower source 1318 to cause an ablation transducer element 1320 toproduce an appropriate amount of ablation (e.g., controlling time,temperature, current, power, etc.). A switch 1322 or valve mayselectively couple the ablation power source 1318 to the ablationtransducer element 1320.

When a polymeric piezoelectric material is used as the force sensortransducer element 1302, it is important to ensure the force sensortransducer element 1302 is sufficiently electrically insulated toeliminate any leakage current. A possible insulating material to use issilicone. Also, integrating an amplifier near the piezoelectric forcesensor transducer element 1302 may improve the circuit performance andmay make the circuit 1300 less susceptible to leakage current.

Although this circuit 1300 uses multiplexing via connectors 1330 a, 1330b to measure the force exerted on the elements, it is also possible toforgo multiplexing and have a circuit dedicated for each element, or acombination of both techniques.

Note that the same piezoelectric sensing grid can also be used inalternate ways to differentiate non-blood tissue from blood. Forexample, it can be used as an ultrasonic transmitter and receiver todifferentiate based on reflection or on damping coefficient.

Frame

The frame provides expansion and contraction capabilities for thecomponent of the medical device (e.g., grid or array of transducerelements) used to distinguish between blood and non-blood tissue. Thetransducer elements used to sense a parameter or characteristic todistinguish between blood and non-blood tissue may be mounted orotherwise carried on a frame, or may form an integral component of theframe itself. The frame may be flexible enough to slide within acatheter sheath in order to be deployed percutaneously. FIG. 2,discussed previously, showed one embodiment of such a frame. Additionalembodiments of frames are shown in FIGS. 14A, 14B, 15A, 15B, 15C, 16Aand 16B.

FIG. 14A shows a frame 1400 made from a number of helical members 1402a, 1402 b (collectively 1402) in an unexpanded configuration andpositioned within a catheter sheath 1404 of a catheter 1408. FIG. 14Bshows the frame 1400 extended outside of the catheter sheath 1404 and inan expanded configuration.

The helical members 1402 may be disposed about a shaft 1410. The helicalmembers 1402 may be positioned between opposing stops 1412 a, 1412 b,which engage the ends of the helical members 1402 to cause expansion.While two helical members are shown, some embodiments may employ agreater or fewer number of helical members 1402.

The frame 1400 is expanded by retracting a shaft 1410. Retracting theshaft 1410 causes the midpoint of the helical members to be forcedoutward and move toward the interior surface of the cavity in which theframe is positioned. FIG. 14B shows that some of the helical members1402 are oriented in a clockwise direction and others are oriented in acounter clockwise direction. The opposing directions cause the helicalmembers 1402 a, 1402 b to cross over and forma grid.

The helical members 1402 may be constructed of many different types ofmaterial including solid wire (such as stainless steel), hollow tube,carbon fiber, or a flexible PCB with a fibreglass or Nitinol backing.The helical members 1402 may form an integral component of the sensingand ablation transducer elements. FIG. 4 provided several example of howelements could be constructed from solid wire, hollow tube, carbonfiber, or flexible PCB. When the transducer elements form an integralcomponent of the frame, the material to be used for the frame requiresproper mechanical and electrical properties. If the device isdistinguishing between blood and non-blood tissue using flow sensing,the material used for the helical members 1402 preferably has asignificant change in resistance with temperature that is independent ofhelical members 1402 deformation. Also, a resistance of several ohms percentimetre or higher is preferable as it will reduce the amount ofcurrent needed to heat the transducer element. The helical members 1402may also act as a support for a secondary assembly that carries thesensing and ablation transducer elements. An example of this is astainless steel or Nitinol structure used to expand transducer elementsmade with a flexible PCB substrate.

FIGS. 15A-15C show a frame 1500, according to another illustratedembodiment.

The frame 1500 includes a single helical member 1502, a plurality ofribs 1504, and a shaft 1506, oriented approximately parallel to alongitudinal axis of a catheter 1508. The sensor and ablation transducerelements are located along the helical member 1502 and ribs 1504.

FIG. 15A shows the frame 1500 in its unexpanded or contractedconfiguration, positioned within a catheter sheath 1510 of the catheter1508. In the unexpanded or contracted configuration, the ribs 1504 arecompressed against the shaft 1506 and the single helical member 1502 iswound around the ribs 1504. The catheter sheath 1510 is insertedpartially into the lumen, cavity, chamber or atrium that the device isto operate in. The frame 1500 is then pushed out of the sheath 1510 intothe chamber and then expanded.

FIG. 15B shows the frame 1500 in a partially expanded configuration. Theframe 1500 is expanded by first unwinding the helical member 1502. Theshaft 1506 is rotated, which causes the helical member 1502 to unwindand expand outward from the shaft 1506.

FIG. 15C shows the frame 1500 in a fully expanded configuration. Theframe 1500 is fully expanded by retracting the shaft 1506, which causesthe ribs 1504 to bow outwards and move both the helical member 1502 andribs 1504 to be proximate to the non-blood tissue that forms theinterior surface of the chamber. The ribs 1504 and helical member 1502may only be physically attached at the proximal and distal ends of theribs 1504 and helical member 1502, or the ribs 1504 may have loopsspaced along their length through which the helical member 1502 slides.

There are several variations on the example shown in FIGS. 15A-15C.These include a frame in which the helical member is inside the ribs,and pushes the ribs outward. Alternatively, a frame may include ahelical member that is positioned inside the ribs, and the ribs are onlyattached at the proximal or distal end.

The same principles regarding construction and composition of the ribsdescribed for the frame 1400 of FIGS. 14A and 14B may be applied to theframe 1500 of FIGS. 15A-15C.

FIGS. 16A and 16B show an embodiment a frame 1600 made using one or moreinflatable members 1602. The particular inflatable member 1602 shown isapproximately spherical in shape, although it is possible to construct aframe using inflatable members that are oblong as well.

FIG. 16A shows the frame 1600 in an inflated or expanded configuration.FIG. 16B shows a cross section of the frame 1600. The preferred methodof expanding this frame 1600 is to inflate via one or more ports 1604with a fluid. A fluid, such as saline, that is not dangerous ifinadvertently released into the body may be particularly suitable. Theport 1604 may be fluidly communicatively coupled to source of fluid, forexample via one or more lumens of a catheter 1606. The source of fluidmay be pressurized. The inflatable member 1602 may be folded inside acatheter sheath 1608 for percutaneous or intravascular delivery. Theinflatable member 1602 may be withdrawn or pushed from the cathetersheath 1608 when in a desired position in the bodily organ.

This inflatable member may have one or more passages, collectively 1610,(only three called out in FIGS. 16A and 16B) opening to the exteriorsurface 1612. The passages 1610 may provide fluid communication throughthe inflatable member 1602. For example, the passages 1610 may connectto a hollow interior cavity 1614. These passages 1610 allow blood toflow through the frame 1600 even when the frame 1600 is inflatedsufficiently to be in contact with the interior surface of the lumen,cavity, chamber or atrium in which the frame 1600 is located. Thus,blood may flow from a downstream side or position, to and open streamside [D1] or position, relative to the position of the frame 1600, evenwhen inflated and in the expanded configuration. Such advantageouslyprevents occlusion.

An advantageous design feature when building an inflatable member thathas interior structures, such as blood flow passages 1610 or an innercavity 1614 is that the walls that form those interior structures shouldbe reinforced to prevent the wall from collapsing or buckling. Suchreinforcement can be accomplished in variety of ways. For example, bycreating the inner walls using much thicker material, creating ribbedwalls with alternating thinner or thicker sections, collectively 1616,(only three called out in FIG. 16B), or reinforcing the walls withspring like wires.

An inflatable frame 1600 as described may be created using a materialsuch as latex. This device may be used as a supporting frame forelements, for example constructed using flexible printed circuit boards.

Joint Assembly

Several of the frames discussed in the preceding section employ jointswhere transducer elements cross over one another. FIGS. 17A-17E andFIGS. 18A-18B show several examples of different structures that can beused.

FIG. 17A shows several strips 1702 a-1702 c (collectively 1702) offlexible printed circuit board substrate at different orientations toone another. Such strips 1702 may be used to build the ribs, struts, orframe members mentioned previously. Where the strips 1702 cross, theymay be joined by a hinge 1704 a, 1704 b (collectively 1704) thatattaches both strips 1702. The hinge 1704 may, for example extendthrough both strips 1702. The 1702 strips are still able to swivelaround the hinge point. The preferred place to join the strips 1702 isat the connecting points between transducer elements 1708 a,1708 b(collectively 1708, only two called out in FIG. 17A). If the transducerelements 1708 are designed to share leads, the hinge can be used toelectrically connect the transducer elements 1708 that have an endcoincident with the joint. Alternatively the transducer elements 1708may be electrically insulated from the hinge 1704 with no electricalcontact points between the strips 1702. The transducer elements 1708between the hinges 1704 may be used to distinguish between blood andnon-blood tissue and/or to ablate. Leads may extend along each strip1702 back to the catheter (not shown in FIG. 17A) and to a controlsystem (not shown in FIG. 17A).

FIG. 17B shows several strands 1722 a-1722 c (collectively 1722) ofcarbon fiber at different orientations to one another. Such strands 1722may be used to build the ribs, struts, or frame members mentionedpreviously. Where the strands 1722 cross, the carbon fiber strands 1722are pinched or crimped 1724 a, 1724 b (collectively 1724) together, forexample by means of a crimping mechanism. The crimping mechanism may bemade from materials such as carbon fibre, carbon paste (cured byheating) metal, or glue. Pinching the carbon fibre together at the jointenables the strands to swivel about the joint. The carbon fibre betweeneach connecting point can be used as a transducer element 1726 (only onecalled out in FIG. 17B) to sense flow, sense temperature and/or toablate. A lead 1728 (only one called out in FIG. 17B) can be connectedat each joint to control the transducer elements 1726 as shown by thecircuit 800 of FIG. 8.

FIG. 17C shows several wires or hollow tubes 1730 a-1730 b (collectively1730) made of material such as stainless steel or Nitinol, at differentorientations from one another. Such wires or tubes 1730 may be used tobuild the ribs, struts, or frame members mentioned previously. Where thewires or tubes 1730 cross, they are connected at joints or connectionpoints 1732 a, 1732 b (collectively 1732) for example by being fusedtogether using spot or laser welding. The wire or tube between eachconnecting point can be used as a transducer element, collectively 1734(only one called out in FIG. 17C), to sense flow, sense temperatureand/or to ablate. A lead, collectively 1736 (only one called out in FIG.17C), can be connected at each joint or connection point 1732 to controlthe transducer elements 1734 as shown by the circuit in FIG. 8.

FIG. 17D shows several strips 1742 a-1742 c (collectively 1742) offlexible printed circuit board substrate at different orientations toone another. Such strips 1742 may be used to build the ribs, struts, orframe members mentioned previously. Where the strips 1742 cross 1744 a,1744 b (collectively 1744), they are not mechanically joined, butallowed to slide over top of each other. Since a fixed hinge point doesnot exist in the configuration, it is necessary to be able to determinewhere the strips 1742 cross when the frame is in the expandedconfiguration inside a body lumen, cavity, chamber or atrium in order toproperly determine the location of openings or ports of the lumen,cavity, chamber or atrium. One method of doing this is to make use ofthe heating and temperature sensing capabilities of the transducerelements 1746 (only one called out in FIG. 17D). Each transducer element1746 should be heated slightly in turn (such as several degrees aboveblood temperature) while other transducer elements 1746 are sensingtemperature. If the transducer element 1746 being heated is located at acrossing point, a different transducer element 1746 sensing temperature,but also located at the same crossing point will sense a temperatureincrease. All or most pairs of transducer elements 1746 that cross maybe determined using such an approach

FIG. 17E shows a flexible printed circuit board substrate 1752 in a leafshape. Such a PCB substrate 1752 is used to cover one portion of theinterior surface of the body cavity. Multiple such PCB substrates may bejoined together as shown in FIG. 2, to cover at least a significantportion of the surface of a lumen, cavity, chamber or atrium. These PCBsubstrates may surround a frame that is used to push them outward andproximate to the surface. The PCB substrates may overlap. Overlappingtransducer elements 1754 a, 1754 b (collectively 1754, only two calledout in FIG. 17E) may be determined using the method described for theembodiment of FIG. 17D.

FIG. 18A shows a frame 1800 formed from metal strips 1802 a-1802 c(collectively 1802) formed to have flexure points 1804. Such strips 1802may be used to build the ribs, struts, or frame members mentionedpreviously. The ribs, struts, or frames have crossing points 1806 a,1806 b (collectively 1806). At the crossing points 1806 the metal strips1802 are fused together using spot welding. The metal strips 1802 areformed to have a flexure 1804 on either side of the crossing point 1806.The flexure 1804 enables the strips 1802 to bend which may be beneficialfor the expansion and contraction of the frame 1800. A portion of thestrip 1802 between each connecting or crossing point 1806 can be used asa transducer element 1808 (only one called out in FIG. 18A) to senseflow, sense temperature and/or to ablate non-blood tissue. A lead 1810(only one called out in FIG. 18A) can be connected at each joint tocontrol the transducer elements 1808 as shown by the circuit in FIG. 8.

FIG. 18B shows a frame 1820 formed from metal strips 1822 a-1822 d(collectively 1822) formed to have slots 1824 (only one illustrated).Such strips 1822 may be used to build the ribs, struts, or frame membersmentioned previously. The ribs, struts, or frames have crossing points1826 a-1826 d (collectively 1826). At the crossing point 1826 of twostrips 1822, one of the strips has a slot 1824 and the other strip 1822slides through the slot 1824. The slot 1824 may be formed in a strip1822 by joining two thin strips 1828 a, 1828 b by spot welds 1830 (onlytwo called out in FIG. 18B). It is possible to connect the control leads1832 to the spot welds 1830 which are located between the crossingpoints 1826 and use the portions of the strips 1822 between eachconnecting or crossing point 1826 as a transducer element to sense flow,sense temperature and/or ablate non-blood tissue. However, this methodwill require approximately 40% more wires than connecting the controlleads at the crossing points.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theinvention can be modified, if necessary, to employ systems, circuits andconcepts of the various patents, applications and publications toprovide yet further embodiments of the invention.

These and other changes can be made to the invention in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the invention to thespecific embodiments disclosed in the specification and the claims, butshould be construed to include all medical treatment devices inaccordance with the claims. Accordingly, the invention is not limited bythe disclosure, but instead its scope is to be determined entirely bythe following claims.

1-69. (canceled)
 70. A medical system comprising: a medical deviceincluding at least a first transducer positionable in at least a portionof a bodily organ; and a computing system coupled to the medical deviceand configured to: determine a tissue dielectric characteristic duringcontact between the at least the first transducer and bodily materialwithin the at least the portion of the bodily organ; generate a map ofat least some of a physical interior surface of a tissue wall of thebodily organ based at least on the determined tissue dielectriccharacteristic; and cause at least one display device coupled to thecomputing system to display output representing at least part of themap.
 71. The medical system of claim 70, wherein the computing system isconfigured to determine the tissue dielectric characteristic at least bydetermining a dielectric constant.
 72. The medical system of claim 70,wherein the determined tissue dielectric characteristic corresponds to achange in a dielectric constant as a function of frequency.
 73. Themedical system of claim 70, wherein the computing system is configuredto determine the tissue dielectric characteristic based at least in parton a signal set indicative of a dielectric constant, the signal setproviding information across a range of frequencies.
 74. The medicalsystem of claim 73, wherein the range of frequencies has a lower boundof 1 KHz.
 75. The medical system of claim 73, wherein the range offrequencies has an upper bound of 100 KHz.
 76. The medical system ofclaim 73, wherein at least some of the frequencies in the range offrequencies are between 1 KHz and 100 KHz.
 77. The medical system ofclaim 73, wherein at least some of the frequencies in the range offrequencies are between 1 KHz and 100 MHz.
 78. The medical system ofclaim 70, wherein the computing system is configured to determine thetissue dielectric characteristic based at least in part on a ratio ofvalues, each value in the ratio of values corresponding to a dielectricconstant.
 79. The medical system of claim 78, wherein the ratio ofvalues is a ratio of (a) a value corresponding to a particulardielectric constant determined at least from a signal indicative of afirst signal frequency, and (b) a value corresponding to a particulardielectric constant determined at least from a signal indicative of asecond signal frequency, the second signal frequency greater than thefirst signal frequency.
 80. The medical system of claim 78, wherein afirst portion of the map of at least some of the physical interiorsurface of the tissue wall of the bodily organ indicates a physicaltissue region of the physical interior surface of the tissue wall of thebodily organ, and a second portion of the map of at least some of thephysical interior surface of the tissue wall of the bodily organindicates a fluid port in the physical interior surface of the tissuewall of the bodily organ, wherein the computing system is configured todetermine the first portion of the map of at least some of the physicalinterior surface of the tissue wall of the bodily organ based on thedetermined tissue dielectric characteristic being based at least in parton a first ratio of values, and wherein the computing system isconfigured to determine the second portion of the map of at least someof the physical interior surface of the tissue wall of the bodily organbased on the determined tissue dielectric characteristic being based atleast in part on a second ratio of values, the second ratio of valuescloser to unity than the first ratio of values.
 81. The medical systemof claim 78, wherein the ratio of values is a ratio of (a) a valuecorresponding to a particular dielectric constant determined at leastfrom a signal indicative of a first signal frequency and (b) a valuecorresponding to a particular dielectric constant determined at leastfrom a signal indicative of a second signal frequency, the second signalfrequency greater than the first signal frequency.
 82. The medicalsystem of claim 70, wherein the computing system is configured todetermine a type of contact between at least part of the medical deviceand tissue in the bodily organ.
 83. The medical system of claim 82,wherein the computing system is configured to generate the map of atleast some of the physical interior surface of the tissue wall of thebodily organ based at least on the determined type of contact betweenthe at least part of the medical device and the tissue in the bodilyorgan.
 84. The medical system of claim 82, wherein the computing systemis configured to determine the type of contact between the at least partof the medical device and the tissue in the bodily organ based at leaston an analysis of the determined tissue dielectric characteristic. 85.The medical system of claim 82, wherein the computing system isconfigured to determine the type of contact between the at least part ofthe medical device and the tissue in the bodily organ at least bydetermining whether the at least part of the medical device is incontact with fluid or non-fluid tissue based at least on an analysis ofthe determined tissue dielectric characteristic.
 86. The medical systemof claim 82, wherein the computing system is configured to determine thetype of contact between the at least part of the medical device and thetissue in the bodily organ at least by determining whether the at leastpart of the medical device is in contact with blood or non-blood tissuebased at least on an analysis of the determined tissue dielectriccharacteristic.
 87. The medical system of claim 78, wherein thecomputing system is configured to determine whether at least part of themedical device is in contact with fluid or non-fluid tissue based atleast on an analysis of the determined tissue dielectric characteristic,wherein the analysis of the determined tissue dielectric characteristicincludes determining that the at least part of the medical device is incontact with non-fluid tissue in a case in which the ratio of values isa first ratio, and wherein the analysis of the determined tissuedielectric characteristic includes determining that the at least part ofthe medical device is in contact with fluid in a case in which the ratioof values is a second ratio, the second ratio closer to unity than thefirst ratio.
 88. The medical system of claim 78, wherein: the ratio ofvalues is a ratio of (a) a value corresponding to a particulardielectric constant determined at least from a signal indicative of afirst signal frequency to (b) a value corresponding to a particulardielectric constant determined at least from a signal indicative of asecond signal frequency, the second signal frequency greater than thefirst signal frequency, the computing system is configured to determinewhether at least part of the medical device is in contact with fluid ornon-fluid tissue based at least on an analysis of the determined tissuedielectric characteristic, the analysis of the determined tissuedielectric characteristic includes determining that the at least part ofthe medical device is in contact with non-fluid tissue in a case inwhich the ratio of values is a first ratio, and the analysis of thedetermined tissue dielectric characteristic includes determining thatthe at least part of the medical device is in contact with fluid in acase in which the ratio of values is a second ratio, the second ratioless than the first ratio.
 89. The medical system of claim 70, whereinthe bodily material is blood.
 90. A method of operating a medical deviceincluding at least a first transducer positionable in at least a portionof a bodily organ, the method executed by a computing system, and themethod comprising: determining a tissue dielectric characteristic duringcontact between the at least the first transducer and bodily materialwithin the at least the portion of the bodily organ; generating a map ofat least some of a physical interior surface of a tissue wall of thebodily organ based at least on the determined tissue dielectriccharacteristic; and causing at least one display device coupled to thecomputing system to display output representing at least part of themap.